1. Field of the Invention
The present invention relates to a scroll compressor which is suitable for use as a compressor for an air conditioner or as an air compressor.
2. Discussion of the Prior Art
FIGS. 3a and 3b show essential portions known scroll compressor which is adapted to be driven at a constant speed. This scroll compressor has a stationary scroll wrap 1a and an orbiting scroll wrap 2a. The orbiting scroll wrap 2a is adapted to make an orbiting motion in sliding contact with the stationary scroll wrap 1a, thereby minimizing the radial gap between both wraps so as to minimize internal leakage of the compressed medium from the compression chamber, thereby improving the compression efficiency.
This condition is realized by the following mechanism. FIGS. 3a and 3b disclose that crankshaft 8 is provided in the upper surface thereof with an elongated bearing-receiving hole 10a offset from the axis of the crankshaft. The hole 10a receives an eccentric bearing 11 not rotatably but slidably in the longitudinal direction of the hole 10a . The elongated hole 10a and the eccentric bearing 11 are so sized that the scroll wraps 1a and 2a contact each other before the eccentric bearing 11 abuts one end wall of the elongated hole 10a . The arrangement also is such that an angle which is not greater than 90.degree. is formed between the longitudinal axis of the elongated hole 10a and the composite force F composed of the force fg produced by the gas pressure acting on an orbiting scroll member 2 carrying the orbiting scroll wrap 2a and the centrifugal force fc acting on the same, at the constant operation speed and under permissible compression load. In normal state of operation, therefore, the composite force F acting on the orbiting scroll member 2 causes the latter to move towards the outer side of the elongated hole 10a along the wall of this hole 10a . In consequence, the orbiting scroll wrap 2a and the stationary scroll wrap 1a are always held in contact with each other at a point which moves progressively without any skip.
This known scroll compressor, however, suffers from the following problems. Namely, the stationary scroll wrap and the orbiting scroll wrap have to be precisely finished, otherwise the position of the point of contact between both scroll wraps is changed not continuously, i.e., the position of the contact point moved in a skipping manner, with the result that the amount S of eccentricity is fluctuated so as to cause a collision between the scroll wraps and, hence, high levels of vibration and noise.
Another problem of this scroll compressor is that, since the described construction is designed for operation at a constant speed, it cannot be applied to variable speed type compressors which nowadays are widely used for air conditioning systems. Namely, when the design is made such that a moderate contact pressure between the orbiting scroll member 2a and the stationary scroll member 1a is obtained at a specific rotation speed, the centrifugal force fc acting on the orbiting scroll member 2 is reduced from the design level when the rotation speed has come down below the specific speed. This undesirably permits the orbiting scroll wrap 2a to oscillate on the stationary scroll wrap 1a or a large radial gap to be formed between both scroll wraps, so as to allow the gas under compression to leak to the low-pressure side so as to impede the operation of the compressor.
Still another problem is that the contact pressure between both scroll wraps tend to become excessively large, resulting in a rapid wear of the wraps, particularly when the compressor is operating at a high speed.